Electric Field Concentration Minimization for MEMS

ABSTRACT

A method and resulting device for reducing an electrical field at an isolation gap in a capacitive actuator includes providing a bottom electrode layer and forming a pattern in the bottom electrode layer having an isolation gap between center and outer electrode components of the patterned electrode. A spacing material is deposited in the isolation gap, the spacing material having a greater height than a remainder of the patterned electrode, and a sacrificial material is deposited conformably on a surface of the patterned electrode and spacing material. The method also includes applying a deformable electrode to a surface of the sacrificial material, whereby removal of the sacrificial and spacing materials results in a greater spacing between the deformable electrode and the electrode layer at a region of the isolation gap than over a remainder of the spacing between the patterned electrode layer and deformable surface.

FIELD OF THE INVENTION

The present invention generally relates to minimizing electric fieldconcentration in an electrostatically actuated device, and morespecifically to increasing a local gap at select positions betweenopposing electrode surfaces relative to a local gap between a remainderof opposing electrode surfaces.

BACKGROUND OF THE INVENTION

In the field of electrostatic actuators, a device can be formed ofrepeating layers of structural, sacrificial, and dielectric materialswhich are patterned and stacked to form complex three dimensionalstructures. Electrostatic actuators can typically include a lowerelectrode opposed by a deformable upper electrode. In order to arrive atsuch a structure, the lower electrode can be patterned to includeisolation gaps between adjacent electrode structures. A sacrificialmaterial can be layered on the lower patterned electrode prior todepositing the upper deformable electrode.

It is a problem in the art, however, that the sacrificial material flowsinto and conforms to a surface variation of the isolation gaps or “cuts”in the electrode. When the upper electrode is deposited, the surfacevariation mimics that of the sacrificial material and in some instancescan even become exaggerated. The flowing of the sacrificial materialinto the isolation gaps therefore causes a gap between the spacedelectrodes to have a smaller distance therebetween at the location ofthe isolation gap. This coupled with a known field concentration at thecorner of the cut in the electrode, combine to make the location a verylikely target for air breakdown, killing the device, or at leastchanging its behavior over time. In addition, the corners can causeproblems in subsequent depositions. For example, a lip can form in asubsequent layer on a high end of the cut, the lip increasing in sizeover multiple depositions. When the top electrode is deposited, it fillsthese cracks and results in very sharp protrusions, which resemblestalactites. It is these “stalactites” which can short the device,causing premature breakdown or at least changing device behavior overtime.

Current solutions to the problem include chemically mechanicallypolishing (CMP) any excess of the deposited sacrificial material,thereby filling holes in the bottom film and eliminating the topographyof the sacrificial material. However, CMP is an expensive andpotentially dirty process. Accordingly, alternatives to CMP are sought.

Thus, there is a need to overcome these and other problems of the priorart and to provide a method and apparatus for minimizing electric fieldconcentration in MEMS devices, particularly at an edge of an isolationgap of a patterned electrode.

SUMMARY OF THE INVENTION

In accordance with the present teachings, a capacitive actuator isprovided.

The exemplary device can include a patterned electrode layer, thepatterned electrode layer comprising a first portion spaced fromadjacent second portions by an isolation gap; and a-deformable electrodespaced from the patterned electrode layer by a greater distance at theisolation gap than over a remainder of the patterned electrode layer.

In accordance with the present teachings, a method for reducing anelectrical field at an isolation gap in a capacitive actuator isprovided.

The exemplary method can include providing a bottom electrode layer;forming a pattern in the bottom electrode layer, the pattern includingan isolation gap between a center and outer electrode components of thepatterned electrode;.depositing a spacing material in the isolation gap,wherein the spacing material has a greater height than a remainder ofthe patterned electrode; depositing and patterning a sacrificialmaterial over an upper surface of the patterned electrode layer, thesacrificial material conforming to a surface of the patterned electrodeand spacing material; and applying a deformable electrode to a surfaceof the sacrificial material, whereby removal of the sacrificial materialand spacing material results in a greater spacing between the deformableelectrode and the electrode layer at a region of the isolation gap thanover a remainder of the spacing between the patterned electrode layerand deformable surface.

In accordance with the present teachings a method for reducing anelectrical field at an isolation gap in a capacitive actuator isprovided.

The exemplary method can include providing a bottom electrode layer;forming a pattern in the bottom electrode layer, the pattern includingan isolation gap filled with a patterning residue, wherein thepatterning residue has a greater height than a remainder of thepatterned electrode; depositing a sacrificial material onto a surface ofthe bottom patterned electrode layer, the sacrificial materialconforming to a surface of the patterned electrode and residue; andapplying a deformable electrode to a surface of the sacrificialmaterial, whereby removal of the sacrificial material and patterningresidue results in a greater spacing between the deformable electrodeand the electrode layer at a region of the isolation gap than over aremainder of the patterned electrode layer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are sectional views of a conventional MEMS devicedepicting an isolation gap before and after removal of sacrificialmaterial, respectively, in accordance with embodiments of the presentteachings;

FIGS. 2A, 2B and 2C are side sectional views depicting known examples ofnon-conformal coatings in accordance with embodiments of the presentteachings;

FIGS. 3A and 3B are side sectional views illustrating a conventionalsolution to correcting non-conformal coatings in accordance withembodiments of the present teachings;

FIGS. 4A and 4B are side sectional views of a fabricated device for usewith embodiments of the present teachings;

FIG. 5 is a fabrication process for the device illustrated in FIGS. 4Aand 4B in accordance with embodiments of the present teachings;

FIGS. 6A and 6B are side sectional views of a fabricated device for usewith embodiments of the present teachings; and

FIG. 7 is a fabrication process for the device illustrated in FIGS. 6Aand 6B in accordance with embodiments of the present teachings.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. However, one of ordinary skill in the art would readilyrecognize that the same principles are equally applicable to, and can beimplemented in devices other than electrostatic actuator type devices,and that any such variations do not depart from the true spirit andscope of the present invention. Moreover, in the following detaileddescription, references are made to the accompanying figures, whichillustrate specific embodiments. Electrical, mechanical, logical andstructural changes may be made to the embodiments without departing fromthe spirit and scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense and thescope of the present invention is defined by the appended claims andtheir equivalents. Wherever possible, the same reference numbers will beused throughout the drawings to refer to the same or like parts.

Embodiments pertain generally to solutions for reducing or eliminatingelectric field concentration at isolation gaps as can occur in patternedelectrodes of an electrostatic actuator. More specifically, thesolutions can be applicable to an electrostatic actuator such as acapacitor with a movable or deformable electrode member.

An electrostatic actuator, such as a known MEMS device, is depicted inFIGS. 1A and 1B, with a portion of FIG. 1B exploded to depict arelationship therein. In particular, a typical MEMS device 100 caninclude a substrate (not shown) with a dielectric spacer 110 thereon. Apatterned electrode 120 can be formed on the spacer 110 to include acenter electrode 122 isolated from a remainder 124 of the patternedelectrode by an isolation gap 126. The center electrode 122 can begrounded as known in the art. The “remainder” 124 of the patternedelectrode 120 can also be referred to as the “outer” or “ungrounded”portions of the patterned electrode. The isolation gap 126 can include astep 127, side walls 128, and corners 129. The step 127 can correspondto a transition between an upper surface of the patterned electrode 120and the side walls 128, while the corner can correspond to a transitionbetween the side walls 128 and dielectric spacer 110.

As depicted in FIG. 1A, a sacrificial material 130 can be deposited overthe patterned electrode 120, while a deformable membrane 140 can bedeposited over the sacrificial material 130. Removal of the sacrificialmaterial 130 results in the configuration of FIG. 1B whereby a dimple142 of the deformable membrane 140 can be deformed to contact theisolated center electrode 122 of the patterned electrode 120. Themembrane 140 can also be grounded so that when it contacts the centerisolated electrode 122, the membrane 140 and the isolated electrode 122are at the same voltage. Deposition of the sacrificial material 130 anddeformable electrode 140 can be in a known manner to achieve thedescribed dimple 142.

In a device such as that depicted in FIGS. 1A and 1B, it will beappreciated that the highest electrical field in the device will occurin areas just on the outer sides of the isolation gap 126. Without undueexplanation, it will be appreciated that these highest electrical fieldsare between the step 127 of the outer electrode 124 and the closestpoint of the membrane 140 as the membrane moves closer to the step ofthe outer electrode.

As further depicted in FIGS. 1A and 1B, flowing of the sacrificialmaterial 130 at the step 127 of the isolation gap 126 results in areduced spacing between the patterned electrode 120 and the deformableelectrode 140 at the region of the isolation gap 126. In order toprevent this location from having a higher field than any other locationin the MEMS Device 100, a surface of the deformable electrode 140 shouldnot dip below or extend beyond a height of the dimple 142. Incombination with the field concentration that occurs at the bottomcorners 129 of the isolation gap 126 in the patterned electrode 120,there is a substantial likelihood of air breakdown, shorting, or similarmalfunctions, which can reduce effectiveness and/or change the behaviorof the device over time, or destroy it entirely.

In the case of multiple subsequent depositions on the patternedelectrode 120, the corners 129 of the isolation gap 126 can cause evenfurther problems. For example, a lip can form in subsequent layers onthe step 127 end of the side wall 128, which becomes exaggerated as thedeposition becomes thicker. When the deform able electrode 140 isdeposited over the sacrificial material 130, it fills these cracks,resulting in sharp protrusions resembling stalactites. The protrusionscan, at a minimum, act as a concentrated point for breakdown, or cause ashort of the device entirely.

Examples of profiles resulting from layers deposited at the step 127and/or isolation gap 126 of the patterned electrode 120 are illustratedin FIGS. 2A, 2B and 2C. In particular, the deposited conformal layer 230depicted in the examples can include a doped oxide such asphosphosilicate glass (PSG). The PSG layer can then act as a “mold” toshape a subsequently deposited layer. This creates the downward spikesof material described as “stalactites” above. In some cases, thestalactite shaped material can extend to the patterned electrode 220 andshort the device. In other cases, even a small lip can touch and shortwhen very little voltage is applied. Even if the stalactite shapedmaterial is very small, the stalactite can still affect robustness ofthe device by acting as field concentration points, lowering the voltageat which the formed device suffers from dielectric breakdown.

FIGS. 3A and 3B are side views depicting a known solution for“planarizing” a sacrificial material 330 prior to depositing adeformable electrode 340. Specifically, a substrate 310 supports apatterned electrode 320 thereon, the patterned electrode including thegrounded center electrode 322 and outer electrode portions 324 spaced bya patterned isolation gap 326. The isolation gap 326 can be formed as aresult of an etching, and a residue or filler 327 can remain therein,polished until its top surface is flat, potentially removing allsacrificial material 330 except that which remains in the isolation gap330. The oxide 327 remaining in the isolation gap 326 can create atotally planar surface so that the electrode cut has no effect on themembrane 340 above. Deposition of the sacrificial material 330 isfollowed by chemical mechanical polishing (CMP) of excess sacrificialmaterial. Additional sacrificial material 330 can optionally bedeposited, particularly in cases where the polishing has removed allsacrificial material 330 except that which remains in the isolation gap330. The deformable electrode 340 is then formed on a planarized surfaceand remains uniformly spaced from a patterned electrode 320 upon removalof the sacrificial material 330. The deformable electrode 340 caninclude a dimple 342 as known in the art. However, the invention alonehas appreciated that CMP is an expensive and potentially dirty process,particularly when used in connection with the known device of FIGS. 3Aand 3B. Accordingly, the present invention provides improvedalternatives to the CMP solution.

Turning now to FIGS. 4A and 4B, a first exemplary approach is described.In the exemplary embodiment, a bottom electrode is patterned byoxidation rather than etching and CMP as occurs in the art.

The structural device 400 of FIGS. 4A and 4B can include an insulatinglayer 410 supported on a substrate (not shown), a patterned electrode420 formed on the grounded electrode, and a deformable electrode 440opposing the patterned electrode. At an intermediate formation of thedevice 400, each of an oxide growth 450 and a sacrificial material 430can be positioned between the patterned electrode 420 and the deformableelectrode 440 (see FIG. 4A).

The insulating layer 410 can include a nitride material and thepatterned electrode 420 can include a polysilicon material having apredefined pattern formed therein. By way of example, the patternedelectrode 420 can include a center isolated electrode 423 spaced fromadjacent outer electrodes 424 of the pattern by an isolation gap 426.The isolation gap 426 can be formed through the patterned electrode 420to a depth revealing a surface of the insulating layer 410. Theisolation gap 426 can be further characterized as including a step 427,side walls 428, and corners 429. The step 427 can correspond to atransition between an upper surface of the patterned electrode 420 andthe side wall 428, while the corner 429 can correspond to a transitionbetween the side wall 428 and the insulating layer 410. It will beappreciated that the terms “step” and “corner” need not assume anangular shape, but can be a curve or other shape.

Patterning of the patterned electrode 420 can be by thermal oxidation,converting portions of the layer to the oxide growth 450 as shown. Theportions converted to oxide growth 450 remain in the isolation gaps 426during subsequent deposition of the sacrificial material 430 anddeformable electrode 440 and will be described further in connectionwith the patterning process.

The deformable upper electrode 440 can include a dimple 442 formed in asurface facing the patterned electrode 420. The deformable upperelectrode 440 can be a polysilicon deposited and patterned in a knownmanner.

In order to define the spacing between the patterned electrode 420 andthe deformable electrode 440, the sacrificial material 430, such asphosphosilicate glass (PSG), can be conformally deposited on thepatterned electrode 420 prior to depositing the deformable electrode440. However, the patterning of the patterned electrode 420 creates acharacteristic surface upon which the sacrificial material 430 flows asdescribed above. Specifically, absent an intervening aspect such asdescribed herein, the PSG will flow into the isolation gaps 426 andresult in the stalactite formations described in connection with theconventional art.

In response to this problem, the patterned electrode 420 herein caninclude the oxide growth 450 in the isolation gap 426, thus creating a“bump” at that location. The conformal PSG contours to the bump of oxidegrowth 450, as does the deposited deformable electrode 440. The bump ofoxide growth 450 increases a spacing between the isolation gap 426 ofthe patterned electrode 420 and a corresponding opposing surface of thedeformable electrode 440 facing the isolation gap as compared to aremainder of the spacing between the patterned and deformableelectrodes, thereby decreasing an electrical field at the region of theisolation gap 426 upon operation of the device. Thus, a predeterminedspacing can be maintained between the patterned electrode 420 anddeformable electrode 440, even at the isolation gap 426 in the patternedelectrode once the sacrificial material is removed.

In order to obtain the described bump of oxide growth 450, the patternedelectrode 420 can be patterned by thermal oxidation. The patternedelectrode 420 can be a polysilicon electrode. Patterning of thepolysilicon electrode by thermal oxidation can convert the desiredpattern portion of the electrode to oxide as depicted in FIG. 4A. Theoxide growth 450 will be substantially thicker than the silicon which itreplaces as a result of the oxidation. In addition, the oxidationprocess proceeds down and slightly sideways through the polysilicon ofthe patterned electrode 420, slowing as it goes, stopping only when ithits the underlying insulating layer 410. The oxidation process resultsin a shallow filleted curvature 460 at the “corner” 429 of the isolationgap where side walls 428 of the isolation gap join with the insulatinglayer 410. This shallow curvature 460 eliminates sharp corners in theisolation gap 426 of the patterned electrode 420, thereby removing fieldconcentration that can occur in the presence of sharp corners. Evenfurther, since the sacrificial material 430 can not flow to form a “lip”on the steps 427 of the isolation gap 426, the subsequently depositeddeformable electrode 440 can not form stalactites within the isolationgap as in prior devices.

Referring now to FIG. 5, a process 500 for fabricating the device ofFIG. 4B will be described. It will be appreciated that while steps aredescribed in an order, certain steps may be added, removed or modifiedwithout departing from the scope of the invention.

In general, the polysilicon on the insulating layer 410 is deposited butnot etched at step 505. Silicon nitride is deposited, typically in alow-pressure chemical vapor deposition (LPCVD) furnace at step 510.Photoresist is then applied and patterned with a photomask at step 515,and the pattern is transferred to the nitride with a reactive ion etch(RIE) at 520. The wafer is then placed in an oxidation furnace (dry orsteam), which converts exposed polysilicon to silicon dioxide at step525. The oxidation proceeds down and slightly sideways through thepolysilicon, slowing as it progresses, and only stopping when it reachesthe underlying nitride. For a thin polysilicon layer (for example about0.3 μm herein), the oxidation can be completed within hours. At step530, the nitride mask can be removed by wet or dry etch, leaving thebump of oxide growth 450 remaining in the isolation gap 426 of thepatterned electrode 420. The rest of the process can proceed in a knownmanner at step 53 5, depositing and patterning multiple layers ofphosphosilicate glass to build up the dimple and establish apredetermined spacing between the patterned electrode and the deformableelectrode, and then depositing and patterning the polysilicon for thedeformable electrode layer at step 540.

Turning now to FIGS. 6A and 6B, an alternative exemplary approach toreducing or eliminating electric field concentration is shown. Thealternative approach can include an additional or extra sacrificialmaterial over steps of an isolation gap as will be further described inthe following.

Initially, FIGS. 6A and 6B can include an insulating layer 61 0supported on a substrate (not shown), a patterned electrode 620 formedon the insulating layer, and a deformable electrode 640 opposing thepatterned electrode.

The insulating layer 610 can include a nitride material and thepatterned electrode 620 can include a polysilicon material having apredefined pattern therein. By way of example, the patterned electrode620 can include a center isolated electrode 622 spaced from adjacentouter electrodes 624 of the pattern by an isolation gap 626. Theisolation gap 626 can be formed through the patterned electrode 620 to adepth revealing a surface of the insulating layer 610. The isolation gap626 can be further characterized as including a step 627, side walls628, and corners 629. The step 627 can correspond to a transitionbetween an upper surface of the patterned electrode 620 and the sidewall 628, while the corner 629 can correspond to a transition betweenside walls 628 and the insulating layer 610. It will be appreciated thatthe terms “step” and “corner” need not assume an angular shape, butcould be a curve or other shape.

Patterning of the patterned electrode 620 can be by etching.

The deformable upper electrode 640 can include a dimple 642 formed in asurface facing the patterned electrode 620. The dimple 642 can have adefined height as known in the art. The deformable upper electrode 640can be a polysilicon material deposited and patterned in a known manner.An etch of the dimple can be accomplished by depositing a layer of oxideequal to a desired dimple height, followed by etching of the dimple.Then, another layer of oxide is deposited to reach a desired total oxidethickness, followed by an anchor etch. An advantage of this process isthat it corresponds to a thickness of the first layer of oxide, yieldingextremely accurate dimple formation.

During formation of the device 600, spacing materials 650, 670 can bedeposited and/or formed in and around the isolation gap 626 of thepatterned electrode 620 and a sacrificial material 630 can be formedover the spacing materials. With such an arrangement, the deformableelectrode 640 can be spaced from the patterned electrode 620 by agreater distance at the isolation gap 626 than over a remainder of thepatterned electrode 620. As described in connection with the exemplaryembodiment of FIGS. 4A and 4B, the intervening spacing materials 650,670 can create a surface in combination with the patterned electrode 620which prevents the sacrificial material 630 from flowing into theisolation gap 626 when the sacrificial material is in a flowable state.

The spacer materials can include a first material 650 deposited in theisolation gap, for example oxide or nitride, and an intermediate layer670 of sacrificial material over the first material 650. In particular,the intermediate layer 670 of sacrificial material can be deposited overthe first material 650, and to a position overlapping the steps 627 ofthe isolation gap 626. The spacer materials 650, 670 combine to form a“bump” at a location of the isolation gap 626. The conformal sacrificialmaterial 630 contours to the “bump”, as does the deposited deformableelectrode 640. The “bump” increases a spacing between the isolation gap626 of the patterned electrode 620 and a corresponding opposing surfaceof the deformable electrode 640 facing the isolation gap as compared toa remainder of the spacing between the patterned and deformableelectrodes, thereby decreasing an electrical field at the region of theisolation gap of the device.

Still further, the first spacing material 650 can be formed bydepositing an oxide, sacrificial material or the like in the isolationgap. Other depositions and patterning techniques are not intended to beexcluded from the instant disclosure The additional intermediate spacingmaterial 670 can be patterned and/or deposited in addition to the firstspacing material 650. The purpose of the additional spacing material 670is to compensate for possible misaligned of patterns with respect to theisolation gap 626.

The intermediate layer of spacing material 670 increases a distancebetween the patterned electrode 620 and the subsequently depositeddeformable electrode 640 at the location of the isolation gap 626 whileallowing for possible misaligned. Similar to the local oxidationprocess, depositing the extra layer of spacing material 670 eliminates avulnerable point in the device, namely the step 627 at the edge of thecenter electrode 622, in a patterned electrode 620 having isolation gaps626. The additional spacing material 670 can be an oxide, such as PSG ortetraethyl orthosilicate (TEOS), silicon nitride, or any otherinsulator.

A method of fabricating the device of FIGS. 6A and 6B is described inconnection with FIG. 7. It will be appreciated that while steps aredescribed in an order, certain steps may be added, removed or modifiedwithout departing from the scope of the invention.

In general, a process 700 for forming the device of FIG. 6B will bedescribed. The polysilicon on the insulating layer 610 is deposited atstep 705. An etching process can take place at step 710, forming thebottom electrode pattern within the insulating layer 610. Subsequent topattering, a first spacing material 650 is deposited into etchedisolation gap 626 of the insulating layer at step 715.

Subsequent to depositing the first spacing material 650 in the isolationgap 626, an additional patterning is performed at 720. At 725, anadditional spacing material 670 is deposited or applied after patterninglayer 620 so that the additional spacing material 670 only remains inareas where there are isolation gaps 626, biased by a few microns(depending upon design rules) to ensure that the isolation gap 626 iscovered, even when misaligned. The additional spacing material 670 canbe any of an extra layer of oxide or an alternative sacrificial materialand can be about 0.3 μm in thickness.

The rest of the process can proceed in a known manner at step 730,depositing and patterning multiple layers of phosphosilicate glass tobuild up the dimple and predetermined spacing between the patternedelectrode and the deformable electrode, and then depositing andpatterning the polysilicon for the deformable electrode layer at step735.

Although the relationships of components are described in general terms,it will be appreciated that one of skill in the art can add, remove, ormodify certain components without departing from the scope of theexemplary embodiments.

It will be appreciated by those of skill in the art that severalbenefits are achieved by the exemplary embodiments described herein andinclude reduced costs, fewer components, elimination of chemicalmechanical polishing, increased accuracy of components, and removal ofalignment errors.

While the invention has been illustrated with respect to one or moreexemplary embodiments, alterations and/or modifications can be made tothe illustrated examples without departing from the spirit and scope ofthe appended claims. In particular, although the method has beendescribed by examples, the steps of the method may be performed in adifferent order than illustrated or simultaneously. In addition, while aparticular feature of the invention may have been disclosed with respectto only one of several embodiments, such feature may be combined withone or more other features of the other embodiments as may be desiredand advantageous for any given or particular function. Furthermore, tothe extent that the terms “including”, “includes”, “having”, “has”,“with”, or variants thereof are used in either the detailed descriptionand the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising.”, And as used herein, the term “one ormore of” with respect to a listing of items such as, for example, “oneor more of A and B,” means A alone, B alone, or A and B.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein. For example, a range of “less than 10” can include any an allsub-ranges between (and including) the minimum value of zero and themaximum value of 10, that is, any and all sub-ranges having a minimumvalue of equal to or greater than zero and a maximum value of equal toor less than 10, e.g., 1 to 5.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims and theirequivalents.

1. A capacitive actuator comprising: a patterned electrode layer, thepatterned electrode layer comprising a first portion spaced fromadjacent second portions by an isolation gap; and a deformable electrodespaced from the patterned electrode layer by a greater distance at theisolation gap than over a remainder of the patterned electrode layer. 2.The capacitive actuator of claim 1, wherein the isolation gap of thepatterned electrode layer is defined by thermal oxidation of apolysilicon electrode layer.
 3. The capacitive actuator of claim 1,wherein the deformable electrode comprises a protruding dimple opposingthe first electrode portion of the patterned electrode layer and adepression in that surface of the deformable electrode opposing theisolation gap.
 4. A method for reducing an electrical field at anisolation gap in a capacitive actuator, the method comprising: providinga bottom electrode layer; forming a pattern in the bottom electrodelayer, the pattern including an isolation gap between a center and outerelectrode components of the patterned electrode; depositing a spacingmaterial in the isolation gap, wherein the spacing material hasapproximately equal or greater height than a remainder of the patternedelectrode; depositing and patterning a sacrificial material over anupper surface of the patterned electrode layer, the sacrificial materialconforming to a surface of the patterned electrode and spacing material;and applying a deformable electrode to a surface of the sacrificialmaterial, whereby removal of the sacrificial material and spacingmaterial results in a greater spacing between the deformable electrodeand the electrode layer at a region of the isolation gap than over aremainder of the spacing between the patterned electrode layer anddeformable surface.
 5. The method of claim 4, wherein the spacingmaterial is a removable oxide material.
 6. The method of claim 4,further comprising depositing an additional layer of spacing material atthe isolation gap over the spacing material, the additional layer ofspacing material overlapping edges of the isolation gap.
 7. The methodof claim 6, wherein the additional layer of spacing material is about0.3 μm thick.
 8. The method of claim 6, wherein the additional layer ofspacing material is deposited to be about 0.3 μm above a surface of thebottom electrode.
 9. The method of claim 6, wherein additional layer ofspacing material comprises an oxide.
 10. The method of claim 4, whereinthe sacrificial material comprises phosphosilicate glass (PSG).
 11. Amethod for reducing an electrical field at an isolation gap in acapacitive actuator, the method comprising: providing a bottom electrodelayer; forming a pattern in the bottom electrode layer, the patternincluding an isolation gap filled with a spacing material, wherein thespacing material has a greater height than a remainder of the patternedelectrode; depositing a sacrificial material onto a surface of thebottom patterned electrode layer, the sacrificial material conforming toa surface of the patterned electrode and spacing material; and applyinga deformable electrode to a surface of the sacrificial material, wherebyremoval of the sacrificial material and spacing material results in agreater spacing between the deformable electrode and the electrode layerat a region of the isolation gap than over a remainder of the patternedelectrode layer.
 12. The method of claim 11, wherein forming the patternin the bottom electrode comprises a thermal oxidation process, therebycreating an oxide deposit as the spacing material in the isolation gap.13. The method of claim 12, further comprising: depositing the bottomelectrode layer free of etching; depositing silicon nitride; applyingphotoresist to the silicon nitride; patterning the photoresist with thebottom electrode photomask; transferring the pattern to the nitride witha reactive ion etch; converting exposed polysilicon at the isolation gapto silicon dioxide in an oxidation furnace; removing the nitride mask;depositing the sacrificial material to a predetermined height; anddepositing and patterning the deformable electrode layer.
 14. The methodof claim 13, wherein depositing silicon nitride comprises depositing ina low pressure chemical vapor deposition furnace.
 15. The method ofclaim 13, wherein the oxidation furnace comprises a dry furnace.
 16. Themethod of claim 13, wherein the oxidation furnace comprises a steamfurnace.
 17. The method of claim 13, wherein removing the nitride maskis with a wet etch.
 18. The method of claim 13, wherein removing thenitride mask is with a dry etch.
 19. The method of claim 111, whereinthe sacrificial material comprises phosphosilicate glass (PSG).